Sliding member and method for manufacturing same

ABSTRACT

A sliding member in which a sliding layer is capable of exhibiting excellent sliding characteristics in terms of seizure resistance, wear resistance and heat resistance.A method for manufacturing the sliding member of the present teachings is a method for manufacturing a sliding member to manufacture a sliding member sliding with a mating material. The manufacturing method includes irradiating particulate ultra high molecular weight polyethylene with radiation rays in a sealed state, and crosslinking the ultra high molecular weight polyethylene, preparing a composition for a sliding layer containing a solid lubricant and a binder resin, and forming a sliding layer sliding with the mating material by providing the composition for a sliding layer on a base material, and obtaining the sliding member. The solid lubricant includes the ultra high molecular weight polyethylene crosslinked during the irradiating and the crosslinking.

TECHNICAL FIELD

The present invention relates to a sliding member and a method for manufacturing the same.

BACKGROUND ART

Conventionally, sliding members disclosed in Patent Literatures Japanese Patent Laid-Open No. 2013-189569 and Japanese Patent Laid-Open No. 2016-69508 are known. These sliding members each include a base material formed of a steel material or an aluminum material, and a sliding layer formed on the base material. An underlayer may be provided between the base material and the sliding layer. The sliding layer contains a binder resin and a solid lubricant. The binder resin is formed of an epoxy resin or the like. The solid lubricant in Patent Literature Japanese Patent Laid-Open No. 2013-189569 is formed from particulate molybdenum disulfide (MoS₂), particulate polytetrafluoroethylene (PTFE), and particulate polyethylene. In recent years, an ultra high molecular weight polyethylene has been studied because of characteristics of self-lubricity and wear resistance, and the solid lubricant in Patent Literature Japanese Patent Laid-Open No. 2016-69508 includes particulate crosslinked ultra high molecular weight polyethylene.

These sliding members can be adopted in a propeller shaft, a piston and the like in which sliding layers slide with mating material. In particular, the sliding layer in Patent Literature Japanese Patent Laid-Open No. 2013-189569 includes polyethylene that has good affinity for lubricants as a solid lubricant, and therefore realizes a low friction coefficient and high wear resistance. Furthermore, the sliding layer in Patent Literature Japanese Patent Laid-Open No. 2016-69508 uses a crosslinked ultra high molecular weight polyethylene as a solid lubricant, and realize not only seizure resistance and wear resistance but also high heat resistance.

However, for the sliding members, further improvement in the sliding characteristics is desired to ensure reliability. In this regard, according to the test result by the inventors, the sliding layer cannot always exhibit high heat resistance when the crosslinked ultra high molecular weight polyethylene is simply irradiated with radiation rays even if the crosslinked ultra high molecular weight polyethylene is adopted as a part of the solid lubricant. In some cases, the crosslinked ultra high molecular weight polyethylene becomes brittle, and lubrication characteristics of the sliding layer rather deteriorate.

SUMMARY OF INVENTION

It is therefore one non-limiting object of the present teachings to provide a sliding member in which a sliding layer can exhibit excellent sliding characteristics in terms of seizure resistance, wear resistance and heat resistance. This object is achieved by the teachings of claim 1. Further developments of the teachings are recited in the dependent claims.

A method for manufacturing a sliding member of the present teachings is a method for manufacturing a sliding member to manufacture a sliding member sliding with a mating material, and includes

a crosslinking step of irradiating particulate ultra high molecular weight polyethylene with radiation rays in a sealed state, and crosslinking the ultra high molecular weight polyethylene,

a composition preparing step of preparing a composition for a sliding layer containing a solid lubricant including the ultra high molecular weight polyethylene crosslinked in the crosslinking step, and a binder resin, and

a sliding layer forming step of forming a sliding layer sliding with the mating material by providing the composition for a sliding layer on a base material, and obtaining the sliding member.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view showing a state of a pin-on-disk reciprocating test in test 1.

FIG. 2 is a sectional view showing a state of a swash plate-shoe test in test 2.

FIG. 3 is a 500-power SEM image photograph in a sliding layer of test 1, in a sliding member of embodiment 1.

FIG. 4 is a 500-power SEM image photograph in a sliding layer in test 1, in a sliding member of embodiment 2.

FIG. 5 is a 500-power SEM image photograph in a sliding layer in test 1, in a sliding member of embodiment 3.

FIG. 6 is a 500-power SEM image photograph in a sliding layer in test 1, in a sliding member of embodiment 4.

FIG. 7 is a 500-power SEM image photograph in a sliding layer in test 1, in a sliding member of comparative example 2.

FIG. 8 is a 500-power SEM image photograph in a sliding layer in test 1, in a sliding member of comparative example 3.

FIG. 9 is a schematic perspective view showing a state of a ring-on-disk friction and wear test in test 4.

FIG. 10 is a schematic perspective view showing a state of a pin-on-disk friction and wear test in test 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <Crosslinking Step>

As means for irradiating particulate ultra high molecular weight polyethylene with radiant rays in a sealed state, (1) a vacuum method to evacuate a container storing particulate ultra high molecular weight polyethylene to reduce the proportion of existence of air, (2) a gas purge method to fill a container with inert gas or nitrogen to discharge air, and the like can be adopted. An atmosphere may include some oxygen without using a vacuum method or a gas purge method, as long as the atmosphere is sealed.

As the radiation rays, X-rays, electron beams, and ion beams can be adopted in addition to α-rays, β-rays, and γ-rays. An amount of radiation rays is expressed as a dose proportional to energy absorbed in a unit mass. A gray (Gy) is a unit that represents an amount of energy absorbed by a certain substance (referred to as an absorbed dose) when the radiation rays strike the substance.

<Composition Preparing Step> (Binder Resin)

A binder resin exhibits a retention property for a solid lubricant that makes it difficult to detach the solid lubricant, durability against a shearing force that repeatedly acts under a layered coating film (hardness as a base), wear resistance with which the binder resin is difficult to break, heat resistance and the like. As the binder resin, a polyimide resin, an epoxy resin, a phenol resin and the like can be adopted. As the polyimide resin, polyamide-imide (PAI), polyimide and the like can be adopted. Considering cost and characteristics, it is optimal to use PAI as the binder resin

(Solid Lubricant)

A solid lubricant is held by the binder resin, and exhibits a low shearing force and a low friction coefficient on an outermost surface. As the solid lubricant, fluororesin, molybdenum dioxide, graphite, ultra high molecular weight polyethylene and the like are adoptable. Fluororesin and ultra high molecular weight polyethylene improve slidability by forming a coating film on a sliding surface of a sliding layer, and transferring to a mating material. Molybdenum dioxide and graphite improve slidability by a crystal structure having a low shearing force, and realizes low friction under a high load. According to test results by the inventors, fluororesin has sliding characteristics such as wear resistance and seizure resistance, but has oil repellency, and has a relatively large lubricating oil contact angle. On the other hand, ultra high molecular weight polyethylene has lipophilic properties though it is inferior to fluororesin in sliding characteristics, and has a relatively small lubricating oil contact angle. Furthermore, as the solid lubricant, melamine cyanurate (MCA), calcium fluoride, and soft metals such as copper and tin can be adopted. In particular, ultra high molecular weight polyethylene that is properly crosslinked hardly liquates from a surface of a sliding layer at high temperatures, and can improve excellent seizure resistance and wear resistance.

The ultra high molecular weight polyethylene before crosslinked preferably has an average molecular weight of 1,000,000 to 7,000,000. Furthermore, a specific gravity of the ultra high molecular weight polyethylene before crosslinked is preferably 0.92 to 0.96. The ultra high molecular weight polyethylene before crosslinked preferably has a particle size less than or equal to 30 μm, and more preferably has a particle size of less than or equal to 15 μm, in terms of surface smoothness and wear resistance.

(Additive, Etc.)

A sliding layer can have an additive in addition to the binder resin and the solid lubricant. As the additive, additives that increase hardness of the sliding layer can be adopted, such as hard particles of titanium dioxide, tricalcium phosphate, alumina, silica, silicon carbide and silicon nitride.

The sliding layer can contain a metal compound containing sulfur such as ZnS and Ag₂S as an extreme pressure agent. Furthermore, the sliding layer can have a surfactant, a coupling agent, a processing stabilizer, an antioxidant and the like.

As a silane coupling agent used for silane coupling treatment, a functional group is preferably an epoxy group. As the silane coupling agent having an epoxy group in the functional group, 2-(3,4-Epoxycyclohexyl) ethyltrimethoxysilane, 3-Glycidoxypropyltrimethoxysilane, 3-Glycidoxypropylmethyldiethoxysilane, and 3-Glycidoxypropyltriethoxysilane are preferable. These silane coupling agents also have excellent storage stability.

<Sliding Layer Forming Step>

As a sliding layer forming step, it is possible to perform viscosity adjustment and density adjustment of a solid content by appropriately diluting a composition for a sliding layer with a solvent such as n-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, or xylene, depending on a kind of a coating method such as spray coating and roll coating. It is possible to form a sliding layer by performing drying and burning after coating a base material with a diluent of the composition for a sliding layer.

EMBODIMENTS (First Experiment)

Hereinafter, embodiments 1 to 4 according to the present teachings, and comparative examples 1 to 3 will be described. First, the following materials were prepared.

Binder Resin: Polyamide-Imide Resin (PAI) Varnish

Solid lubricant: particulate ultra high molecular weight polyethylene (UHPE particle), particulate fluorine compound (PTFE particle), MoS₂, graphite

A plurality of bags formed of vinyl that are capable of being airtight and are of the same size were prepared, a fixed amount of UHPE particles were put into each of these bags, and respective bags were evacuated under the same conditions. Thereafter, each of the bags was put into an electron beam irradiation device, and UHPE particles were irradiated with electron beams as radiation rays at an absorbed dose (kGy) shown in Table 1. In this manner, UHPE particles of crosslinked products No. 1 to 6 were obtained. UHPE particles of an uncrosslinked product were not irradiated with electron beams. UHPE particles of an unsealed crosslinked product were irradiated with electron beams in a state open to the atmosphere, that is, without being put into the bag.

Table 1 shows melting points (° C.), gel fractions (%), and average particle sizes (μm) of the respective UHPE particles. Furthermore, Table 1 also shows a melting point (° C.) and an average particle size (μm) of PTFE particles.

TABLE 1 Particulate ultra high molecular weight polyethylene (UHPE particle) Fluorine Crosslinked Crosslinked Crosslinked Crosslinked Crosslinked Crosslinked Unsealed compound Uncrosslinked product product product product product product crosslinked PTFE particle product No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 product Electron beam — — Sealed Sealed Sealed Sealed Sealed Sealed Open to irradiation atmosphere atmosphere Electron beam 0 0 60 80 100 300 500 1000 100 absorbed dose [kGy] Melting point 323.8 134.6 132.0 131.6 131.2 128.2 126.4 123.0 133.2 [° C.] Gel fraction — 0 26 69 66 69 68 71 0 [weight %] Average 5 10 10 10 10 10 10 10 10 particle size [μm]

Here, measurement conditions of the melting point are as follows.

Analysis equipment: DSC Q2000 (TA instrument)

Heating rate: 5° C./minute (After a temperature was raised to 210° C., the temperature was cooled to 30° C. at −20° C./minute, and measurement was performed again.)

Atmosphere: N₂

Sample weight: 5 mg±0.1 mg each

Melting point reading conditions: a melting peak temperature when measuring again

The gel fractions were measured as follows. First, each powder was pressed at a constant pressure while being heated at 180° C. to 230° C., and thereby a sheet having a thickness of 0.3 mm was formed. From each sheet, a small piece of 0.3 g was cut. Each small piece was put into a flask, and 500 milliliters of p-xylene was added into the flask. While heating each flask to 130° C., the mixture in the flask was stirred for four hours to dissolve each small piece. The solution was filtered with a wire mesh having a mesh of 106 μm while the solution is in a high temperature state of 130° C. Insoluble matters on the wire mesh were dried under vacuum at 140° C. for three hours, and a weight (g) of the insoluble matters after the room temperature was measured. Subsequently, the gel fraction was obtained by a formula of gel fraction (%)=insoluble matter weight (g)×100/0.3 (g).

As the composition preparing step, PAI varnish and each solid lubricant were compounded at a compounding ratio shown in Table 2, and after the compound was stirred well, the compound was passed through three roll mills, whereby compositions for the sliding layers in embodiments 1 to 4 and comparative examples 1 to 3 were prepared. The solid lubricant is formed from PTFE particles, UHPE particles, MoS₂ and graphite. The UHPE particles are any one of an uncrosslinked product, crosslinked products No. 1 to 4 or an unsealed crosslinked product.

TABLE 2 Embodiment Embodiment Embodiment Embodiment Comparative Comparative Comparative Volume % 1 2 3 4 example 1 example 2 example 3 PAI varnish 50 50 50 50 50 50 50 Solid PTFE particle — — — — 18 — — lubricant UHPE Uncrosslinked particle product — — — — — 18 — Crosslinked No. 1 18 — — — — — — product No. 2 — 18 — — — — — No. 3 — — 18 — — — — No. 4 — — — 18 — — — Unsealed — — — — — — 18 Molybdenum disulfide 18 18 18 18 18 18 18 Graphite 14 14 14 14 14 14 14 Volume % of solid lubricant per 100% 100 100 100 100 100 100 100 by volume of PAI resin

The following sliding layer forming step was performed. First, the respective compositions for sliding layers were diluted with a solvent to make dilutions, the respective dilutions were coated on the base material formed of a steel material, after which, drying was performed, and burning was performed at 220° C. for 1.5 hours. Thereafter, surface grinding was performed to make film thicknesses the same, and sliding layers of the film thickness of 15 μm were formed. In this manner, the respective sliding members of embodiments 1 to 4 and comparative examples 1 to 3 were obtained.

The respective sliding members are each formed of the base material and the sliding layer formed on the base material. The sliding layer contains the binder resin and the solid lubricant. The respective sliding members were provided to tests 1 to 3 as follows.

<Test 1 (Pin-On-Disk Reciprocating Test)>

The test is to confirm a liquation (residual) state of the UHPE particles in the sliding layer of each of the sliding members. In other words, as shown in FIG. 1, each sliding member 10 is placed on a plate 1 in which a top surface can be heated. In this state, in each sliding member 10 has a sliding layer 10 a as the top surface. On the sliding layer 10 a, a pin 2 made of SUJ2 with a curvature of a tip end of 10R is reciprocated under conditions of a load of 350 gf, a reciprocation distance 20 mm, a speed of 2 Hz, and a number of reciprocations of 3500. At this time, a temperature of a substrate surface is controlled to 80° C., and a lubricant 3 containing hydrocarbon oil is dropped onto the sliding layer 10 a. The test was performed to the sliding members of embodiments 1 to 4 and comparative examples 1 to 3.

<Test 2 (Swash Plate-Shoe Test 1)>

The test is to evaluate a friction coefficient and seizure under a dry environment in a swash plate type compressor. In other words, as shown in FIG. 2, a base material 20 was formed into a shape of a swash plate of a compressor, a sliding layer 20 a was formed on each of the base materials 20, and a swash plate was obtained as described above. Meanwhile, a shoe 5 made of SUJ2 was held by a holding tool 4. Subsequently, the swash plate was rotated at a sliding speed of 10 m/second, a load of 1960 N was applied to between the swash plate and the shoe 5, and a time (second) required for the swash plate and the shoe 5 to seize was investigated. The test was performed to the sliding members of embodiments 1 to 4 and comparative examples 1 to 3.

<Test 3 (Swash Plate-Shoe Test 2)>

The test is to evaluate seizure at a time of applying a load stepwise under lubrication in oil in a swash plate type compressor. In other words, as shown in FIG. 2, the base material 20 was formed into a shape of a swash plate of a compressor, a sliding layer 20 a was formed on each of the base materials 20, and a swash plate was obtained as described above. Meanwhile, a shoe 5 made of SUJ2 was held by a holding tool 4. Subsequently, the swash plate was rotated at a sliding speed of 7 m/second while refrigerating machine oil was attached to a surface of the swash plate by amount of 6 g/minute, a load of 400 N was applied to between the swash plate and the shoe 5 every five minutes, and a load (N) under which the swash plate and the shoe 5 were seized was investigated. The test was performed to the sliding members of embodiments 1 to 4 and comparative examples 1 to 3.

Table 3 shows results of the tests. Furthermore, remaining states of UHPE particles in the sliding layers of the respective sliding members of embodiments 1 to 4 and comparative examples 2 and 3 after test 1 were confirmed by SEM images. FIG. 3 shows a 500-power SEM image photograph in the sliding layer of test 1, in the sliding member of embodiment 1. FIG. 4 shows a 500-power SEM image photograph in the sliding layer of test 1, in the sliding member of embodiment 2. FIG. 5 shows a 500-power SEM image photograph in the sliding layer of test 1, in the sliding member of embodiment 3. FIG. 6 shows a 500-power SEM image photograph in the sliding layer of test 1, in the sliding member of embodiment 4. FIG. 7 shows a 500-power SEM image photograph in the sliding layer of test 1, in the sliding member of comparative example 2. FIG. 8 shows a 500-power SEM image photograph in the sliding layer of test 1, in the sliding member of comparative example 3.

TABLE 3 Test 2 Test 3 Friction Seizure time Seizure load coefficient [second] [N] Embodiment 1 0.033 510 4000 Embodiment 2 0.033 479 5600 Embodiment 3 0.032 524 5600 Embodiment 4 0.033 451 4800 Comparative 0.033 465 3600 example 1 Comparative 0.038 235 4000 example 2 Comparative 0.036 293 3600 example 3

As can be seen from Table 3, the sliding members of embodiments 1 to 4 can exhibit excellent seizure resistance and wear resistance. It is presumed the reason of this is that since the sliding members of embodiments 1 to 4 adopt UHPE particles irradiated with radiation rays in the sealed state, the UHPE particles are hardly oxidized, and are properly crosslinked.

In particular, the sliding layers in the sliding members of embodiments 2 to 4 exhibit excellent seizure resistance and wear resistance. It is presumed this is because the sliding members of embodiments 2 to 4 each adopt crosslinked UHPE particles having a melting point of more than or equal to 128.2° C. and less than or equal to 132.0° C., and a gel fraction of more than or equal to 26% by having an absorbed dose of electron beams of more than or equal to 60 kGy and less than or equal to 300 kGy as shown in Table 1, so that the UHPE particles hardly liquate and drop out of the surface of the sliding layer at high temperatures, as shown in FIGS. 4 to 6.

On the other hand, as can be seen from Table 3, the sliding members of comparative examples 2 and 3 each have a low seizure load, and poor seizure resistance. It is presumed this is because the sliding member of comparative example 2 adopts UHPE particles of an uncrosslinked product, and therefore the UHPE particles easily liquate and drop out of the surface of the sliding layer at high temperatures as shown in FIG. 7. Furthermore, it is presumed this is because the sliding member of comparative example 3 adopts UHPE particles of an unsealed crosslinked product having a gel fraction of 0%, so that the UHPE particles are oxidized and are not properly crosslinked, and the UHPE particles easily liquate and drop out of the surface of the sliding layer at high temperatures as shown in FIG. 8.

Accordingly, it is found that in the sliding members of embodiments 1 to 4, in particular, the sliding members of embodiments 2 to 4, the sliding layers can exhibit excellent sliding characteristics in terms of self-lubricity, wear resistance and heat resistance. Therefore, it is found that, if these sliding member are adopted in swash plates or the like of compressors, more excellent compressors can be obtained.

(Second Experiment)

Next, embodiments 5 to 18 according to the present teachings, and comparative examples 4 to 8 will be described. First, as in the first experiment, as a composition preparing step, PAI varnish and each solid lubricant were compounded at a compounding ratio shown in Tables 4 to 6, and after the compound was stirred well, the compound was passed through three roll mills, whereby compositions for the sliding layers in embodiments 5 to 18 and comparative examples 4 to 8 were prepared. Subsequently, as in the first experiment, a sliding layer forming step was performed. In this manner, respective sliding members of embodiments 5 to 18 and comparative examples 4 to 8 were obtained.

TABLE 4 Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Volume % 5 6 7 8 9 10 11 PAI varnish 50  50 50  50 50 50 50 Solid PTFE particle — — — — — — — lubricant UHPE Unccosslinked product — — — — — — — particle Crosslinked No. 1 — — — — — — — product No. 2 — — — — — — — No. 3 25  35 28  23 223 15 10 No. 4 — — — — — — — No. 5 — — — — — — — No. 6 — — — — — — — Molybdenum disulfide 15  9 0  5 22.5 15 10 Graphite 10  6 22  19 5 20 30 Volume % of solid lubricant per 100% 100  100 100 100 100 100 100 by volume of PAI resin

TABLE 5 Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Volume % 12 13 14 15 16 17 18 PAI varnish 80 50 50 50 50 80 80 Solid PTFE particle — — — — — — — lubricant UHPE Uncrosslinked product — — — — — — — particle Crosslinked No. 1 — — — — — — — product No. 2 — — — — — — — No. 3 10  5 10 15 25 7.5 10 No. 4 — — — — — — — No. 5 — — — — — — — No. 6 — — — — — — — Molybdenum disulfide  0 26 23 25 25 7.5 10 Graphite 10 19 17 10  0 5  0 Volume % of solid lubricant per 100% 25 100  100  100  100  25 25 by volume of PAI resin

TABLE 6 Comparative Comparative Comparative Comparative Comparative Volume % example 4 example 5 example 6 example 7 example 8 PAI varnish  50  50 40  40  40 Solid PTFE particle — — — — — lubricant UHPE Uncrosslinked product — — — — — particle Crosslinked No. 1 — — — — — product No. 2 — — — — — No. 3 — — 22.5  30  30 No. 4 — — — — No. 5  18 — — — — No. 6 —  18 — — — Molybdenum disulfide  18  18 22.5  30  0 Graphite  14  14 15  0  30 Volume % of solid lubricant per 100% 100 100 150 150 150 by volume of PAI resin

The respective sliding members of embodiments 1 to 4 and comparative examples 1 and 2 obtained by the first experiment, and the respective sliding members of embodiments 5 to 18 and comparative examples 4 to 8 obtained by the second experiment were provided to tests 4 and 5 as follows.

<Test 4 (Ring-On-Disk Friction and Wear Test: Under Dry Environment>

The test is to evaluate wear resistance under a certain level of a dry environment in the sliding layers of the respective sliding members. In other words, as shown in FIG. 9, a sliding layer 30 a of each of the sliding members is formed on a top surface of a base material 30 formed of S45C. A film thickness of the sliding layer 30 a is approximately 20 μm. In this state, a ring 6 is placed on a top surface of the sliding layer 30 a of each of the sliding members. The ring 6 made of S45C is rotated under conditions of a contact pressure of 5.4 MPa, a sliding speed of 0.9 m/second, and a sliding distance of 500 m. A specific wear amount (×10⁻⁶ mm³/N·m) of the sliding layer 30 a during this while was measured. The test was performed to the sliding members of embodiments 1 to 18 and comparative examples 1, 2 and 4 to 8.

<Test 5 (Pin-On-Disk Friction and Wear Test: Under Oil Environment)>

The test is to evaluate wear resistance under a certain level of an oil environment in the sliding layers of the respective sliding members. In other words, as shown in FIG. 10, a sliding layer 40 a of each of the sliding members is formed on a top surface of a base material 40 formed of S45C. A film thickness of the sliding layer 40 a is approximately 15 μm. In this state, a pin 7 is placed on a top surface of the sliding layer 40 a of each of the sliding members. The pin 7 made of SUJ2 in which a curvature of a tip end is 10R is rotated under conditions of a load of 20N, a sliding speed of 0.25 m/second, and a sliding distance of 22.6 m. At this time, 5 mg of a refrigerator oil 8 was dropped onto the sliding layer 40 a, and a wear depth of the sliding layer 40 a during this while was measured. The test was performed to the sliding members of embodiments 1 to 18 and comparative examples 1, 2 and 4 to 8.

Table 7 shows results of test 4 and test 5 in the sliding members of embodiments 1 to 4 and comparative examples 1 and 2. Tables 8 to 10 show results of test 4 and test 5 in the sliding members of embodiments 5 to 18 and comparative examples 4 to 8.

TABLE 7 Embodiment Embodiment Embodiment Embodiment Comparative Comparative 1 2 3 4 example 1 example 2 Test 4 Specific wear amount × 10{circumflex over ( )}−6 2.4 2.8 2.2 5.6 5.7 3.6 [mm3/N · m] Test 5 Wear depth [μm] 2.9 2.2 4.1 2.7 20.1 9.1

TABLE 8 Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment 5 6 7 8 9 10 11 Test 4 Specific wear amount ×10{circumflex over ( )}−6 1.3 0.7 0.7 0.5 2.9 3.2 1.6 [mm3/N · m] Test 5 Wear depth [μm] 4.7 2.6 4.3 4.2 4.4 3.4 2.4

TABLE 9 Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment 12 13 14 15 16 17 18 Test 4 Specific wear amount × 10{circumflex over ( )}−6[mm3/N · m] 2.3 1.5 3.4 2.8 2.2 7.8 5.1 Test 5 Wear depth [μm] 1.0 11.3 17.5 17.3 15.0 1.0 1.0

TABLE 10 Comparative Comparative Comparative Comparative Comparative example 4 example 5 example 6 example 7 example 8 Test 4 Specific wear amount × 10{circumflex over ( )}−6[mm3/N · m] 9.7 7.7 4.4 4.9 6.3 Test 5 Wear depth [μm] 11.5 11.0 14.5 12.6 14.1

In evaluating the wear resistance of the sliding members of embodiments 1 to 18, wear resistance of the sliding member of comparative example 2 was used as a criteria. The reason of this is that while the UHPE particles are properly crosslinked in the sliding members of embodiments 1 to 18, the UHPE particles are not crosslinked in the sliding member of comparative example 2 as can be seen from Tables 2 and 4 to 6, and therefore presence or absence of crosslinking of the UHPE particles was adopted as the criteria.

As can be seen from Tables 7 to 10, in the respective sliding members of embodiments 1 to 18, the specific wear amounts are less than 3.6 (×10⁻⁶ mm³/N·m), or wear depths are less than 9.1 (μm) when the results of tests 4 and 5 in the sliding member of comparative example 2 are the standards. In other words, the sliding members of embodiments 1 to 18 can exhibit excellent wear resistance under the dry environment or under the oil environment. It is presumed the reason of this is that since the sliding members of embodiments 1 to 18 adopt the UHPE particles irradiated with radiation rays in the sealed state, the UHPE particles are hardly oxidized, and are properly crosslinked. In particular, in the sliding members of embodiments 1 to 3 and 5 to 12, the sliding layers exhibit excellent wear resistance under the dry environment and under the oil environment.

Furthermore, it is presumed that since the sliding members of embodiments 1 to 18 adopt the crosslinked UHPE particles having the melting points of more than 126.4° C. and less than or equal to 132.0° C., and gel fractions of more than or equal to 26% by having the absorbed doses of electron beams of more than or equal to 60 kGy and less than 500 kGy as shown in Table 1, the UHPE particles hardly liquate and drop out of the surfaces of the sliding layers at high temperatures.

On the other hand, as can be seen from Tables 7 to 10, the sliding members of comparative examples 1, 2, 4 and 5 have the specific wear amounts of more than or equal to 3.6 (×10⁻⁶=³/N·m), and wear depths of more than or equal to 9.1 (μm), in the results of tests 4 and 5. Accordingly, the sliding members of comparative examples 1, 2, 4 and 5 have poor wear resistance under either the dry environment or the oil environment as compared with the sliding members of embodiments 1 to 18. It is presumed that the sliding member of comparative example 1 adopts a fluorine compound (PTFE particles) instead of the UHPE particles which are properly crosslinked, and therefore has poor wear resistance. It is presumed that the sliding member of comparative example 2 adopts the uncrosslinked UHPE particles with a melting point of 134.6° C., and therefore the UHPE particles easily liquate and drop out of the surface of the sliding layer at high temperatures. Furthermore, it is presumed that since in the sliding members of comparative examples 4 and 5, the absorbed doses of electron beams are more than or equal to 500 kGy, the crosslinked UHPE particles are brittle, and wear resistance of the sliding members rather deteriorate.

Accordingly, it is found that in the sliding members of embodiments 1 to 18, the sliding layers can exhibit excellent wear resistance under the dry environment or under the oil environment. In particular, in the sliding members of embodiments 1 to 3 and 5 to 12, the sliding layers can exhibit excellent wear resistance under the dry environment or under the oil environment.

In the sliding layer, the solid lubricant is preferably more than or equal to 25% by volume and is less than or equal to 100% by volume with respect to the binder resin, and the ultra high molecular weight polyethylene is preferably more than or equal to 5% by volume and is less than or equal to 35% by volume with respect to all solid components in the sliding layer. More specifically, the sliding members of embodiments 1 to 18 can exhibit excellent wear resistance under the dry environment or under the oil environment to the sliding members of comparative examples 6 to 8. In other words, in the siding members of comparative examples 6 to 8, the specific wear amounts are more than 3.6 (×10⁻⁶ mm³/N·m), and the wear depths are more than 9.1 (μm) in the results of tests 4 and 5. It is presumed that since in the sliding members of comparative examples 6 to 8, the solid lubricants were 150% by volume with respect to the binder resins, the binder resins were unable to retain the solid lubricants, and the solid lubricant dropped out of the surface of the sliding layer at high temperatures.

In the sliding layer, molybdenum disulfide is preferably less than or equal to 26% by volume with respect to all solid components in the sliding layer. In this case, in the sliding layer, the wear resistance can be more improved under the dry environment or under the oil environment. Furthermore, as in the sliding members of embodiments 7 and 12, molybdenum disulfide does not have to be included in the solid lubricant.

In the sliding layer, the ultra high molecular weight polyethylene is preferably more than or equal to 23% by volume and less than or equal to 35% by volume with respect to all solid components in the sliding layer, and molybdenum disulfide is preferably less than or equal to 15% by volume with respect to all solid components in the sliding layer. In this case, the sliding layer can further improve the wear resistance under the dry environment in particular. More specifically, the sliding members of embodiments 5 to 8 can exhibit excellent wear resistance under the dry environment. In the siding members of embodiments 5 to 8, the specific wear amounts are within a range of 0.5 to 1.3 (×10⁻⁶=³/N·m), and show remarkable effects as compared with the other embodiments in test 4.

In the sliding layer, graphite is preferably more than or equal to 5% by volume and less than or equal to 30% by volume with respect to all solid components in the sliding layer. In this case, the sliding layer can further improve the wear resistance under the dry environment or under the oil environment. Furthermore, graphite does not have to be included in the solid lubricant as in the sliding members of embodiments 16 and 18.

Although the present teachings have been described above in line with embodiments 1 to 18, it is needless to say that the invention is not limited to the above-described embodiments 1 to 18, but may be appropriately modified in application without departing from the gist of the teachings.

For example, in the present teachings, it is possible to perform a degreasing step of contacting alkali or the like to the base material to enhance adhesion of the base material and the sliding layer. Furthermore, it is also possible to form an underlayer formed from phosphate such as zinc phosphate, and manganese phosphate after the degreasing step to further enhance adhesion of the base material and the sliding layer.

The present teachings are applicable to various sliding members. 

1. A method for manufacturing a sliding member to manufacture a sliding member sliding with a mating material, comprising: irradiating particulate ultra high molecular weight polyethylene with radiation rays in a sealed state, and crosslinking the ultra high molecular weight polyethylene; preparing a composition for a sliding layer containing a solid lubricant including the ultra high molecular weight polyethylene crosslinked during the irradiating and the crosslinking, and a binder resin; and forming a sliding layer sliding with the mating material by providing the composition for a sliding layer on a base material, and obtaining the sliding member.
 2. The method for manufacturing a sliding member according to claim 1, wherein the irradiating and the crosslinking is performed under a condition that an absorbed dose of electron beams as the radiation rays is more than or equal to 60 kGy and less than 500 kGy.
 3. A sliding member comprising a base material, and a sliding layer formed on the base material, and containing a binder resin and a solid lubricant, the sliding layer sliding with a mating material, wherein the solid lubricant includes crosslinked ultra high molecular weight polyethylene that is particulate, and has a melting point that is more than 126.4° C. and less than or equal to 132.0° C.
 4. The sliding member according to claim 3, wherein the ultra high molecular weight polyethylene has a gel fraction of more than or equal to 26%.
 5. The sliding member according to claim 3, wherein in the sliding layer, the solid lubricant is more than or equal to 25% by volume and less than or equal to 100% by volume with respect to the binder resin, in the sliding layer, the binder resin is polyamide-imide, and the ultra high molecular weight polyethylene is more than or equal to 5% by volume and less than or equal to 35% by volume with respect to all solid components in the sliding layer.
 6. The sliding member according to claim 5, wherein the solid lubricant further includes molybdenum disulfide, and in the sliding layer, the molybdenum disulfide is less than or equal to 26% by volume with respect to all solid components in the sliding layer.
 7. The sliding member according to claim 6, wherein in the sliding layer, the ultra high molecular weight polyethylene is more than or equal to 23% by volume and less than or equal to 35% by volume with respect to all solid components in the sliding layer, and the molybdenum disulfide is less than or equal to 15% by volume with respect to all solid components in the sliding layer.
 8. The sliding member according to claim 5, wherein the solid lubricant further includes graphite, and in the sliding layer, the graphite is more than or equal to 5% by volume and less than or equal to 30% by volume with respect to all solid components in the sliding layer.
 9. The sliding member according to claim 3, wherein the ultra high molecular weight polyethylene has a gel fraction of more than or equal to 26%, wherein in the sliding layer, the solid lubricant is more than or equal to 25% by volume and less than or equal to 100% by volume with respect to the binder resin, in the sliding layer, the binder resin is polyamide-imide, and the ultra high molecular weight polyethylene is more than or equal to 5% by volume and less than or equal to 35% by volume with respect to all solid components in the sliding layer.
 10. The sliding member according to claim 9, wherein the solid lubricant further includes molybdenum disulfide, and in the sliding layer, the molybdenum disulfide is less than or equal to 26% by volume with respect to all solid components in the sliding layer.
 11. The sliding member according to claim 10, wherein in the sliding layer, the ultra high molecular weight polyethylene is more than or equal to 23% by volume and less than or equal to 35% by volume with respect to all solid components in the sliding layer, and the molybdenum disulfide is less than or equal to 15% by volume with respect to all solid components in the sliding layer.
 12. The sliding member according to claim 9, wherein the solid lubricant further includes graphite, and in the sliding layer, the graphite is more than or equal to 5% by volume and less than or equal to 30% by volume with respect to all solid components in the sliding layer.
 13. The sliding member according to claim 6, wherein the solid lubricant further includes graphite, and in the sliding layer, the graphite is more than or equal to 5% by volume and less than or equal to 30% by volume with respect to all solid components in the sliding layer. 